Your retaining walls already failing is one clue.
This order of operations you are suggesting is another one.
You don't pick projects by technical difficulty in the dirt work world. When you have multiple projects on a site, you start where it makes sense because of the site. Typically, you start where you need to cut because the material is going to be needed elsewhere. You have to plan where you will store the material until you need it. You want to work from the back of the property to the access so you may have to include access work into your order. But retaining walls do not like loaded equipment driving around on them or near their load column. Also your plan needs to consider water runoff. You don't want to have to clean up your material off the property of the next 3 neighbors down the hill.
I am probably leaving some things off, but dirtwork is one of those things that look much more simple than it actually is and mistakes can be really expensive. That combination is not good for the typical homeowner. In true irate fashion, I hope you do it and ignore me as long as you promise to post progress and problems in camarogenius fashion.